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Date: Thu, 26 Oct 2017 20:10:36 +1100
From: "Tobin C. Harding" <me@tobin.cc>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
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On Thu, Oct 26, 2017 at 09:00:03AM +0200, Greg KH wrote:
> On Thu, Oct 26, 2017 at 12:59:08AM +0200, Jason A. Donenfeld wrote:
> > On Thu, Oct 26, 2017 at 12:27 AM, Tobin C. Harding <me@tobin.cc> wrote:
> > > How good is unlikely()?
> > 
> > It places that branch way at the bottom of the function so that it's
> > less likely to pollute the icache.
> 
> But always measure it.  Lots of times (old numbers were 90% or so), we
> get the marking wrong, so please, always benchmark the thing to verify
> it actually is doing what you think it should be doing, otherwise it
> could make the code worse.

Does this come under 'premature optimization is the root of all evil'?

Should we be leaving out things like unlikely() and __read_only until
the code has been profiled?

thanks,
Tobin.